It is known that one can use for the low-pressure polymerization of olefins catalytic systems containing a compound of a transition metal and an organo-metallic compound.
It is also known from Belgian Pat. 705,220 that one can use as compound of the transition metal of the catalytic systems mentioned above a solid obtained by reacting a halogenated compound of a transition metal with an oxygenated compound of a divalent metal such as magnesium. The catalytic systems thus obtained are very active if they are compared with those in which the halogenated compound of a transition metal is used as it is.
In Belgian Pat. No. 767,586, catalytic systems are described, one of the components of which is prepared by reacting an organic oxygenated compound of a divalent metal with an alkylaluminium halide, separating the product of this reaction and reacting it then with a halogenated compound of a transition metal. These catalytic systems are also characterized by a high activity.
However, such catalytic systems with a high activity and others of the prior art lead to polymers which have an important defect. In point of fact, while their physical properties and more particularly their mechanical properties are on the whole quite satisfactory, their resistance to impact is sometimes insufficient. Now, the resistance to impact is an essential quality for polyolefins because they are used mainly for manufacturing objects which are used for handling (crates, tanks, pellets) and packing (bottles, films) which are subject to impact when they are used.